Stripline directional coupling device

ABSTRACT

A directional coupling device is provided having a first and second conductor of a first pair of conductors extending parallel to and closely spaced from one another. A second pair of conductors having a first and second conductor extending parallel to and closely spaced from one another are spaced laterally from the first and second conductors of the first pair of conductors, respectively. A first end of the first conductor of the first pair of conductors is electrically connected to the first end of the second conductor of the second pair of conductors. Also, the first end of the first conductor of the second pair of conductors is electrically connected to a first end of the second conductor of the first pair of conductors. The first and the second conductors of the first pair of conductors at the second end thereof respectively include an input and an output means. The second end of each of the first and second conductors of the second pair of conductors includes a terminating means so that electrical pulses arriving thereat will be terminated.

United States Patent [191 Nick [1;] 3,764,941 [451 Oct; 9,1973

[ STRIPLINE DIRECTIONAL COUPLING DEVICE [75] Inventor: Howard H. Nick,Poughkeepsie,

[73] Assignee: International Business Machines Corporation, Arrnonk,N.Y.

22 Filed: Dec. 8, 1972 [21] Appl. No.: 313,298

[52] U.S. Cl..- 333/10, 333/1, 333/84 M [51-] Int. Cl. H01p 5/14, HOlp3/08 [S8] Field of Search 333/10, 9, 1,84 M

[56] References Cited UNITED STATES PATENTS 3,460,069 8/1969 Uberbacheret a1. 333/10 Primary Examiner-Rudolph V. Rolinec AssistantExaminer-Marvin Nussbaum Attorney-W. N. Barrett, Jr. et al.

[57] ABSTRACT A directional coupling device is provided having a firstand second conductor of a first pair of conductors extending parallel toand closely spaced from one another. A second pair of conductors havinga first and second conductor extending parallel to and closely spacedfrom one another are spaced laterally from the first and secondconductors of the first pair of conductors, respectively. A first end ofthe first conductor of the first pair of conductors is electricallyconnected to the first end of the second conductor of the second pair ofconductors. Also, the first end of the first conductor of the secondpair of conductors is electrically connected to a first end of thesecond conductor of the first pair of conductors. The first and thesecond conductors of the first pair of conductors at the second endthereof respectively include an input and an output means. The secondend of each of the first and second conductors of the second pair ofconductors includes a terminating means so that electrical pulsesarriving thereat will be terminated.

8 Claims, 5 Drawing Figures STRIPLINE DIRECTIONAL COUPLING DEVICE Thisinvention relatesv to directional couplers and more particularly, to animproved stripline directional coupling device which can be used tofulfill high density connector requirements.

With the increase in operating speed of devices, such as computers, intothe nanosecond range, it has been foundthat directional couplers can beutilized to couple high speed pulses to and from the transmission lineswith respective sub-lines leading to and from various peripheraldevices. In U. S. No., No, 3,516,065 filed Jan. 13, 1967, a system fortransmitting digital data between a plurality-of data processing devicesusing striplinedirectional couplers is disclosed. The use ofthedirectional coupler in the system eliminates the stub length limitationsand allows any stub or stublines connecting individual devices to thetransmission line'tobe limited in length only by the degradation of asignal passed along the line.

As is known, a stripline directional coupleris a device wherein twoparallel adjacent printed circuit striplines, sandwiched betweentwoground planes,-are inductively and capacitively coupled sothat'theedges of a first pulse of fast rise and fall timecharacteristics, propagating along one line, produce a positive pulse Itis an object of'the present invention-to provide a directional couplerin which unwanted cross coupling signals are practically eliminated.

It is another object of the present invention to'provide a striplinedirectional coupler in which shorter lengths of conductive couplingelements are used. It is a futher object of the present inventiontoprovide a striplingdirectional coupler which'can be packand'a negativepulse in the other line. The lines are coupled such that the thusproduced pulses propagate along the, second line in a'direction oppositeto the direction in which the first pulse propagates along the firstline. The energy transferred be'tweenthe conducting segments of thetwo-element directional coupler is effected by the various physicalcharacteristics of the directional couplersuch as the length, width anddistance between the couplingsegments.Accordingly, the long couplingelement lengths needed to obtain a good energytransfer betweenthesegments of the coupler introduces obvious disadvantages inpackagingthe twoelement directional coupler, especially where a large numberfofsuch devices are to be combined in the same package. I

The directional coupler conductors have two general configurations whenused as a connecting device. For example, the coplanar directionalcoupler consists of parallel lengths of stripline conductor located inthe same plane and spaced adjacent to each other. The other knownarrangement is the broadside directional coupler in which the conductorsare located broadside to one another in adjacent parallel planes so thatthe coupling is between the facing surfaces of the coupling segmentsrather than coupling from edge to edge as is the case in the coplanardirectional coupler. Packaging a plurality of the broadside directionalcouplers introduces the problem of unwanted edge coupling between thecoplanar adjacent conductive segments. This cross coupling seriouslyimpacts the packaging density of the broadside directional coupler.

There are a number of inherent advantages to using the directionalcoupler as a connector rather than the direct line connection that isnormally used. The socalled loose coupling provides isolation betweenislands of logical functions electrically and, thus, overcomes some ofthe present day power problems. Actually, the loose coupling deviceprovides the necessary isolation and matched impedance to allow forwelldefined, almost noiseless, less power consumption signaltransmission.

aged in a much smaller space and at a much greater density.

Briefly, a directional coupling device is provided for transmittingsignals into and out of circuit modules of the type havingahigh densityconnector requirement. The coupler-contains a first and second conductorof a first pair of conductorswhich extend :parallel to and closelyspaced from one another. The coupler also contains a first and secondconductor of a second pair of conductors which extend parallel to andclosely spaced from another and later-allyspaced from thefirst andsecond conductors of the first pair of conductors, re-

spectively. A first'end'of the first conductor of the first pair ofconductors is connected to a'first end ofthe second conductor of thesecond pair'of conductors by a first electrical connectionuAlso, thefirst endof the first conductor of the second pair of conductors isconnected to the first end of the secondconductor of the firstpair ofconductors by a second electrical connection. The second ends of thefirst and second conductors of the'first pair of conductors includes aninput and BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematicdiagram of the prior art twoelement broadside directional couplershowing the input and output wave forms thereof;

FIG. 2 is across-sectional diagram taken along the line 2--2 of FIG. 1identifying the various dimensions;

FIG. 3 is a schematicdiagram of the four element directional coupler ofthe invention showing the input and output wave forms thereof;

FIG. 4 is a cross-sectional diagram taken along the lines 44 of FIG. 3indicating the various dimensions of the elements in the invention;

FIG. 5 is a schematic diagram showing a pair of the four elementdirectional couplers and indicating the interaction with one another.

Referring to FIG. 1, there is shown a schematic diagram of the prior arttwo-element stripline directional coupler which consists of twostripline conductive segments l0 and 12 extending parallel to andclosely spaced from one another from an end A to an end B. Theseconductors or conductive segments 10 and 12 are located broadside to oneanother and closely spaced. Usually, the conductors are mounted in asubstrate 14 made of a dielectric material such as epoxy glass and arearranged between two ground plates 16 and 18 which usually consist ofsheets of copper arranged on either side of the pair of conductors. Eachconductive element and 12 has a terminal 20,22 at the end B of thecoupler serving as an input or output terminal. Each conductor 10, 12has a terminating resistance 24, 26 connected at the A end of thecoupler which matches the coupler to the characteristic impedance of theline to which it is connected. The coupling takes place along the lengthof the segments 10, 12. The coupler operation as defined depends uponthe steepness of the incident pulse rise time. The width or duration ofthe pulse produced by the coupling is determined by the length of thetwo segments 10, 12. The performance of the coupler is described by theimpedances offered to signals on the transmission line and the couplingratio, which are determined by the widths of the lines in the coupledregion, the thickness of the lines, the distance between ground planes,the distance between conductive elements and the relative dielectricconstant of the material. It has been determined that coupling segmentsof electrical length L will produce a pulse having a time duration equalto 2L. For example, a one volt amplitude ideal step function inputsignal applied to the input terminal of segment 10, when the-coupler hasa coupling ration of one to four and an electrical length L of twonanoseconds, will produce an output pulse having a time duration of fournanoseconds and a pulse amplitude of A of a volt. The input pulse canbegenerated by a driver connected to the input to one of the conductiveelements. As is shown in FIG. 1 by arrows, the coupled pulse travels inan opposite direction in the conductive segment 12 to the direction oftravel in the coupling segment 10. It will be appreciated, that eitherof the conductive segments 10 and 12 can serve as the input and likewisethe other would serve as the output. A stripline coupler is operated bythe edge of the wave passing along one of the lines and this wave edgeshould have a rise or fall time that is twice as fast as thetimeduration of the pulse induced by coupling in order that the relationshipof the height of th induced pulse be related to the height of thedriving pulse in the manner defined by the coupling ratio. The variouscritical dimensions of the directional coupler for proper operation areindicated in the cross-sectional diagram of the prior art directionalcoupler shown in FIG. 2.

Packaging of these prior art directional couplers presents a problem inthat cross coupling takes place between the couplers when the devicesare packaged within coupling distance of one another. Considering thecase where a broadside directional coupler, shown in FIG. I, is locateddirectly adjacent a similar device, the one volt ramp input pulse willnot only couple to the stripline located broadside thereto but will alsocouple to an adjacent stripline that is within lateral couplingdistance. The one volt pulse would produce a V4 volt pulse travelling inthe opposite direction along any adjacent laterally spaced stripline.This A volt pulse for example would be seen at the input of the adjacentdirectional coupler and would produce essentially a signal to noiseratio of l to 4. The V4 volt pulse travelling in the opposite directiontowards the output of the second conductor of the first directionalcoupler will also produce a l/l6 V pulse in the second conductor of theadjacent device which travels in the opposite direction, thus travellingtowards the terminating resistance where it is terminated. It shouldalso be appreciated that the second directional coupling device inputpulse likewise causes a coupling signal travelling towards the input ofthe adjacent coupler. This unwanted coupling considered to be cross-talkor noise effectively limits any high density packaging of directionalcouplers.

The four element directional coupler, forming the present invention, isshown schematically in FIG. 3. The arrangement consists of a first pairof stripline conductive elements 30, 32 spaced parallel to one anotherand extending from an end A to an end B. These first and secondconductive elements, 30, 32 are closely spaced from one another with thebottom surface of the first conductor 30 facing the top surface of thesecond conductor 32 of the device. Similarly, a second pair ofconductive stripline elements 34, 36 are located laterally adjacent thefirst and second elements 30, 32 of the first pair. The first conductiveelement 34 of the second pair of conductors is located adjacent to andlaterally displaced from the first conductor 30 in the first pair ofconductors. This distance is within electrical coupling distance. As amatter of fact, the lateral distance is made as small as possible sothat a large number of directional coupler devices can be packaged in asmall space. The second conductor 36 of the second pair of conductors islocated adjacent the second conductor 32 of the first pair of conductorsso that the first and second pairs of conductors lay parallel to oneanother side by side. The second pair of conductors 34, 36 are spacedparallel to one another and have the broadside surfaces facing withincoupling distance of one another. The first conductive element 30 of thefirst pair of conductors has an electrical connection 38 extending fromone end thereof designated as the B end in FIG. 3 to a similar end ofthe second conductor 36 of the second pair of conductors. Similarly, thefirst conductor 34 of the second pair of conductors has an electricalconnection 40 extending from one end thereof, the B end, to the adjacentend of the second conductor 32 of the first pair of conductors. Theother end of the first conductor 30 of the first pair of conductors hasan input terminal 42 for receiving input pulses. This end is designatedas the A end in FIG. 3. Likewise, the second conductor 32 of the firstpair of conductors has an output terminal 44 at the A end of thedirectional coupler device. Each of the conductors 34, 36 of the secondpair of conductors has a terminating resistor 46, 48 at the ends thereofadjacent to the input and output terminals 42, 44 of the first pair ofconductors at the A end of the device. It will be appreciated that thedirectional coupler device is embedded in a dielectric material 50 (seeFIG. 4) for operation in this invention. It has been found that ceramichaving a dielectric constant of 9.5 provides the best operation. Theceramic material 50 containing the conductive elements of thedirectional coupler are sandwiched between an upper and lower groundplane conductor 52, 54. These ground planes 52, 54 can consist of thinsheets of copper. The characteristic impedance of the coupled lines Z isdetermined by the various dimensions and values of the directionalcoupler. For example, the characteristic impedance Z isv dependent onthe width W of the coupled lines, the space S between coupled lines, thespacing D between ground planes, the thickness t of striplines, therelative dielectric constant E of the medium filling the region betweenthe lines and the region between the lines and the ground planes. In atypical situation where W 3 mils, S 4.295 mils, D

596.9551 mils, 1 mil, E; 9.5 then Z, 79.1809 ohms. It should be notedthat the length of the conductive element shown in FIG. 4 is less thanthe length of the conductive element shown in the prior art directionalcoupler of FIGS. 1 and 2. Although the overall length dimension isreduced, it will be appreciated that the directional coupler of FIG. 3has an additional pair of striplines 34, 36 added which, by theelectrical connections 38, 40 from the B ends, essentially compensatefor the loss of length.

In describing the operation of the invention, as is shown in FIG. 3, wewill consider the coupling ratio as being one to four so that a one voltramp input will couple to the adjacent lines a 41 volt pulse. Thus,applying the one volt ramp to the input terminal 42 of the firstconductive element 30 of the first pair of conductors, as shown in FIG.3, produces a /i volt pulse proceeding in the opposite direction towardsthe output terminal 44 of the second conductor 32 of the first pair ofconductors. The one volt input signal also continues through theconnection 38 from the B end of the first conductor 30 of the firstpairof conductors to the B end of the second conductor 36 of the secondpair of conductors where the one volt ramp travels along the conductorinto the terminating resistance 48 at the A end of the second conductiveelement 36 of the second pair. This one volt ramp proceeding along thesecond conductor 36 of the second pair causes a 54 volt pulse to becoupled into the first conductive element 34 of the second pairtravelling in the opposite direction. This volt pulse will travelthrough the connection 40 from the first conductive element 34 of thesecond pair to the second conductive element 32 of the first pair whereit travels towards the output terminal 44 forming the output pulse. Itshould be noted that the A volt pulse in travelling along any conductiveelement causes a coupling tothe adjacent elements of a positive andnegative pulse of.1/l6 of a volt.

Accordingly, the ,4 volt pulse coupled into the sec ond conductiveelement 32 of the first pair of conductors will cause coupling of H1 6volt pulses to the coplanar adjacent conductive element which is thesecond conductive element 36 of the second pair wherein the H16 voltpulses travel toward the B end of the directional coupler through theinterconnecting wire 38 and towards the A end of the coupler along thefirst conductor 30 of the first pair of conductors. These l/ 16 of avolt pulses can be easily handled by the driver, and accordingly, thesignal-to-noise ratio can be considered to be 1 to 16 which appears tobe favorable in comparison to the l to 4 signal-to-noise ratio of theprior art directional coupler. Similarly, the volt pulse causes a 54 Vpulse to be coupled laterally from the first conductor 30 of the firstpair of conductors to the first conductor 34 of the second pair. The /4V pulse causes a 1/16 of a volt pulse to be coupled into the secondconductor 36 of the second pair travelling towards the B end so that itpasses through the electrical connection 38 at the B end to the firstconductor 30 of the first pair where it travels towards the driver andis dissipated therein.

The most important advantage of the arrangement can be realized when anumber of such devices are packaged in a small space. In FIG. 5, thereare shown two directional coupler devices each of which is exactly thesame as the directional coupler device described in connection with FIG.3. Considering the coupling interaction caused by the first or left handcoupler, the one volt pulse travelling towards the terminating resistor48a in thesecond conductive element 36a of the second pair of conductiveelements 340, 36a will cause a 4 volt pulse coupling into a laterallyadjacent element which is the second conductive element-32b of the firstpair'of conducting elements 30b, 32b of the second directional coupleror right hand directional coupler in FIG. 5. As this A wave pulse willbe travelling towards the B endof the conductive element 32b and will,therefore, pass through the electrical connection 40b to the firstconductive element 34b of thesecond pair of conductors where it travelstowards the A end and is thus terminated in the terminating resistor46b. Again the 56. volt pulse travelling towards the B end in the secondconductor 32b-of the first pair will give rise by coupling to a 1/16volt pulse travelling towards the A end in the first conductive element30b of the first pair of conductors. As previously mentioned, this 1/ 16volt pulse will be dissipated in the driver circuits. The V4 volt pulsetravelling towards the A end of the first conductor 34b of the secondpair of conductors gives riseto l /16volt pulses in the second conductor36b of the second pair which is travelling towards the B end, and whichpasses through the electrical connection 38b and travels towards the Aend or input end of the first conductor 30b of the first pair ofconductors where, similarly, it is dissipated. Thus, the signal appliedto the first directional coupler in the pair of directional couplersshown in FIG. 5 causes lateral coupling with a closely spaced seconddirectional coupler, however, the-laterally coupled pulsesareterminated.

The coupling interaction with the first directional coupler caused bythe application of a signal input to the second directional coupler ofthe pair of directional couplers, shown in FIG. 5, will now beinvestigated. The one volt ramp input at the input terminal 42b of thefirst conductive element 30b of the first pair of conductors throughlateral coupling causes a V4 volt pulse in the first conductor 34a ofthe second pair of conductors of the first coupler but travellingtowards the A end where it is terminated in the-terminating resistor460. This coupled A volt pulse in the first conductive ele ment 34a ofthe second pair of conductors gives rise to 1/ 16 of a volt pulsestravelling the opposite direction, that is, towards the B end of thesecond conductor 36a of the second pair of conductors of the firstdirectional coupler which, via the electrical connection 38a, isconnected to the first conductor 30a of the first pair of conductorstravelling towards the input 420 end where, as previously mentioned, itis dissipated in the driver. In FIG. 5, thre is included only thosevoltages which are due to the crosstalk or interaction of the twodirectional couplers shown. The important thing to note is that theinteraction between the two directional couplers causes a A of a voltpulse which, in both directional couplers, is terminated by aterminating resistor. The l/l6 volt pulses caused by the V4 volt pulsesby either broadside coupling or lateral coupling create no particularproblemsince they are either terminated by terminating resistances ordissipated in the input circuitry. Thus, a directional coupler arrangedas described in connection with FIG. 3 can be closely packaged withother similar directional couplers as shown in FIG. 5 without creatingany spacing limitations because of coupling interactions such ascrosstalk.

While the invention has been particularly shown and described withreference to a preferred embodiment thereof, it will be understood bythose skilled in the art that the foregoing and other changes in formand detail may be made therein without departing from the spirit ndscope of the invention.

What is claimed is:

l. A directional coupling device for connecting signals into and out ofcircuit modules having a high density connector requirement comprising:

a first and second conductor of a first pair of conductors extendingparallel to and closely spaced from one another;

a first and second conductor of a second pair of conductors extendingparallel to and closely spaced from one another and laterally spacedfrom said first and second conductors, respectively;

a first electrical connection extending from a first end of said firstconductor of said first pair of conductors to a first end of said secondconductor of said second pair of conductors;

a second electrical connection extending from the first end of saidfirst conductor of said second pair of conductors to a first end of saidsecond conductor of said first pair of conductors;

input means connected to the second ends of said first conductor of saidfirst pair of conductors;

output means connected to the second end of said second conductor ofsaid first pair of conductors and terminating means connected at thesecond ends of said first and second conductors of said second pair ofconductors for terminating electrical pulses arriving thereat so thatpulses applied at said input are coupled to said output and laterallycoupled pulses are attenuated and terminated in said terminating means.

2. A directional coupling device according to claim 1, wherein saidfirst and second conductor of said first pair of conductors and saidfirst and second conductor of said second pair of conductors aresandwiched between first and second ground conductor planes.

3. A directional coupling device according to claim 1, wherein saidfirst and second pairs of conductors are embedded in a dielectricmaterial.

4. A directional coupling device according to claim 3, wherein saiddielectric material is ceramic.

5. A directional coupling device according to claim 1, wherein saidfirst and second conductors of said first and second pairs of conductorsare printed line conductors of the same length, width and thickness.

6. A directional coupling device according to claim 5, wherein saidfirst and second conductors of said first pair of conductors are spacedbroadside to one another within pulse coupling distance and said firstand second conductors of said second pair of conductors are spacedbroadside to one another within pulse coupling distance and spacedcoplanar within coupling distance to said first and second conductors,of said first pair, respectively.

7. A directional coupling device according to claim 1, wherein saidterminating means connected to the second end of said first and secondconductors of said second pair of conductors is a resistor having avalue equal to the characteristic impedance of the line to which thedirectional coupler is to be connected.

8. A directional coupling device according to claim 1, wherein aplurality of directional coupling devices are placed side by side sothat the first and second conductors of said first pair or conductors ofeach directional coupling device are spaced within pulse couplingdistance from the first and second conductors of said second pair ofconductors of the adjacent directional coupling device so that pulsescoupled between directional coupling devices are attenuated andterminated.

1. A directional coupling device for connecting signals into and out ofcircuit modules having a high density connector requirement comprising:a first and second conductor of a first pair of conductors extendingparallel to and closely spaced from one another; a first and secondconductor of a second pair of conductors extending parallel to andclosely spaced from one another and laterally spaced from said first andsecond conductors, respectively; a first electrical connection extendingfrom a first end of said first conductor of said first pair ofconductors to a first end of said second conductor of said second pairof conductors; a second electrical connection extending from the firstend of said first conductor of said second pair of conductors to a firstend of said second conductor of said first pair of conductors; inputmeans connected to the second end of said first conductor of said firstpair of conductors; output means connected to the second end of saidsecond conductor of said first pair of conductors and terminating meansconnected at the second ends of said first and second conductors of saidsecond pair of conductors for terminating electrical pulses arrivingthereat so that pulses applied at said input are coupled to said outputand laterally coupled pulses are attenuated and terminated in saidterminating means.
 2. A directional coupling device according to claim1, wherein said first and second conductor of said first pair ofconductors and said first and second conductor of said second pair ofconductors are sandwiched between first and second ground conductorplanes.
 3. A directional coupling device according to claim 1, whereinsaid first and second pairs of conductors are embedded in a dielectricmaterial.
 4. A directional coupling device according to claim 3, whereinsaid dielectric material is ceramic.
 5. A directional coupling deviceaccording to claim 1, wherein said first and second conductors of saidfirst and second pairs of conductors are printed line conductors of thesame length, width and thickness.
 6. A directional coupling deviceaccording to claim 5, wherein said first and second conductors of saidfirst pair of conductors are spaced broadside to one another withinpulse coupling distance and said first and second conductors of saidsecond pair of conductors are spaced broadside to one another withinpulse coupling distance and spaced coplanar within coupling distance tosaid first and second conductors, of said first pair, respectively.
 7. Adirectional coupling device according to claim 1, wherein saidterminating means connected to the second end of said first and secondconductors of said second pair of conductors is a resistor having avalue equal to the characteristic impedance of the line to which thedirectional coupler is to be connected.
 8. A directional coupling deviceaccording to claim 1, wherein a plurality of directional couplingdevices are placed side by side so that the first and second conductorsof said first pair or conductors of each directional coupling device arespaced within pulse coupling distance from the first and secondconductors of said second pair of conductors of the adjacent directionalcoupling device so that pulses coupled between directional couplingdevices are attenuated and terminated.